Diabetes mellitus is a disorder in which the pancreas cannot create sufficient insulin (Type I or insulin-dependent) and/or in which insulin is not effective (Type II or non-insulin-dependent). In the diabetic state, the patient or user suffers from high blood sugar, which can cause an array of physiological derangements associated with the deterioration of small blood vessels, for example, kidney failure, skin ulcers, or bleeding into the vitreous of the eye. A hypoglycemic reaction (low blood sugar) can be induced by an inadvertent overdose of insulin, or after a normal dose of insulin or glucose-lowering agent accompanied by extraordinary exercise or insufficient food intake.
Conventionally, a person with diabetes carries a self-monitoring blood glucose (SMBG) monitor, which typically requires uncomfortable finger pricking methods. Due to the lack of comfort and convenience, a person with diabetes normally only measures his or her glucose levels two to four times per day. Unfortunately, such time intervals are so far spread apart that the person with diabetes likely finds out too late of a hyperglycemic or hypoglycemic condition, sometimes incurring dangerous side effects. It is not only unlikely that a person with diabetes will become aware of a dangerous condition in time to counteract it, but it is also likely that he or she will not know whether his or her blood glucose value is going up (higher) or down (lower) based on conventional method. Diabetics thus may be inhibited from making educated insulin therapy decisions.
Another device that some diabetics used to monitor their blood glucose is a continuous analyte sensor, e.g., a continuous glucose monitor (CGM). A CGM typically includes a sensor that is placed invasively, minimally invasively or non-invasively. The sensor measures the concentration of a given analyte within the body, e.g., glucose, and generates a raw signal that is generated by electronics associated with the sensor. The raw signal is converted into an output value that is rendered on a display. The output value that results from the conversion of the raw signal is typically expressed in a form that provides the user with meaningful information, and in which form users become familiar with analyzing, such as blood glucose expressed in mg/dL.
The above discussion assumes a reliable and true raw signal is received by the electronics. In some cases, faults or errors are encountered and the signal is no longer reliable and true. Prior art approaches to detecting such are generally of a “one-size-fits-all” approach, as is systems' response to the same.
Faults or errors may be caused in a number of ways. For example, they may be associated with a physiological activity in the host, e.g., metabolic responses, or may also be associated with an in vivo portion of the sensor as the same settles into the host environment. They may also be associated with transient events within the control of a patient, or associated with the external environment surrounding the device. Other such are also seen.
Additionally, in the case of glucose monitoring, as glucose levels and patterns vary from patient-to-patient and even within a patient from day-to-day, noise may be difficult to differentiate from large glucose swings. Similarly, a solution that is best for a patient with stable glucose at one particular time may not be the best solution for the same or different patient at or near hypoglycemia or hyperglycemia, for example.